Cross-carbanion coupling at a rare-earth center

Although reductive elimination of two carbanions at a transition metal center to forge one C–C bond is a fundamental process, the analogous process is missing at a rare-earth metal center. Here, we report a reductive-elimination-type reaction of a dienyl anion and a benzyl anion at a rare-earth center enabled by redox metal-ligand cooperativity where the dienyl group serves as both the coupling partner and electron reservoir. Based on this discovery, we were able to establish the efficient rare-earth-mediated 1,4-hydroalkylation of benzylic C–H bonds of 2-substituted azaarenes across polysubstituted 1,3-diene units. The broad substrate scope, including functional groups incompatible with transition metals, demonstrates the generality of the process and its promising synthetic applications. The reductive-elimination-type reaction at the rare-earth center discovered here represents a new elementary reaction in rare-earth organometallic chemistry and is expected to inspire the general development of rare-earth-promoted cross-nucleophilic coupling.